Generally, a fuel tank capable of accommodating fuel required to operate an engine is mounted in a vehicle and an apparatus for sensing a fuel level capable of sensing a residual amount of fuel is mounted in a fuel tank accommodating liquid fuel so as to inform a driver of the residual amount of fuel.
The apparatus for sensing a fuel level in a fuel tank is classified into a mechanical apparatus for sensing a fuel level and an electronic apparatus for sensing a fuel level.
The mechanical apparatus for sensing a fuel level senses a fuel level by changing a resistance value according to a change in a height of a floater floating in liquid fuel, which has been most prevalently used due to being a low price.
The electronic apparatus for sensing a fuel level directly senses a height of liquid fuel without separate floater.
FIG. 1 shows a mechanical apparatus for sensing a fuel level according to the related art.
The mechanical apparatus for sensing a fuel level according to the related art has a case 1 as shown in FIG. 1.
Further, the mechanical apparatus for sensing a fuel level includes a resistance substrate 2 that is mounted in the case 1 and radially formed within a predetermined angle range.
In addition, the mechanical apparatus for sensing a fuel level includes an arm 3 of which one side is fixed with a floater 3a and the other side is rotatably supported to the case 1.
Further, the mechanical apparatus for sensing a fuel level includes a wiper 4 that rotates together with the arm 3 while being fixed to the arm 3 and contacts the resistance substrate 2.
The case 1 and the resistance substrate 2 disposed therein are fixed to the fuel tank and the arm 3 and the wiper 4 rotates together by moving the floater 3a upward or downward according to the amount of fuel.
Therefore, a contact projection 4a of the wiper contacts different positions of the resistance substrate 2 while rotating within a predetermined angle range in a state in which the contact projection 4a contacts a radiation circuit 2a of the resistance substrate 2.
As a result, the resistance substrate 2 variably shows a resistance value according to the residual amount of fuel, thereby displaying the residual amount of fuel on an instrument panel of a vehicle.
As shown in FIG. 2, the apparatus for sensing a fuel level is generally mounted in a fuel pump module 5 to be mounted in the fuel tank.
However, the apparatus for sensing a fuel level in a fuel tank according to the related art has a problem in that the resistance substrate and the wiper showing different resistance values due to a contact thereof may be rapidly corroded due to a contact portion thereof always exposed to fuel or air and may have reduced durability due to abrasion caused by a continuous contact between the resistance substrate and the wiper.
These problems may lead to situations where the residual amount of fuel is not accurately sensed.
Recently, bio fuel, or the like, has been developed. When the bio fuel is used, the corrosion and abrasion may be more rapidly progressed.
As an apparatus for sensing a fuel level so as to solve these problems, there is a “Device for sensing fuel level for fuel tank of vehicle” filed by the applicant of the present invention and registered as Korean Patent No. 0712605.
The technology prevents the resistance substrate or the wiper from contacting with the fuel in the fuel tank and from being abraded due to the friction of the resistance substrate and the wiper by injecting and sealing a lubricant solution and an anti-rusting solution (hereinafter, referred to as “filling solution”) into a space in which the resistance substrate and the wiper are disposed.
However, the related art may cause situations where the space in which the filing liquid is filled is not in a completely sealed state and the filling solution is frequently leaked from a point (bottom point), which is a gap that prevents the sealing state, such that the filling solution may not demonstrate its own function.
Despite of the above-mentioned problems, it is difficult to confirm the sealing state. As a result, defective products may be delivered and economic losses may be caused due to the delivery of defective products.
Meanwhile, in the case of the apparatus for sensing a fuel level using the above-mentioned filling solution, there is a problem in that the residual amount of fuel may not be smoothly sensed under a low temperature condition of about 30° C. below zero due to low temperature characteristics of the filling solution (see FIG. 5).
Further, the apparatus for sensing a fuel level in a fuel tank having a floater according to the related art, even though the residual amount of fuel is a reference value or more or a reference value or less, the arm rotates within a set range.
The reason is that when the wiper connected to a shaft rotates above the set range, failure may occur.
In particular, when the arm rotates so that the floater may contact the bottom surface of the fuel tank, such that the residual amount of fuel is not smoothly sensed and noise may occur due to a collision of the floater with the bottom surface of the fuel tank at the time a vehicle is traveling.
The method of rotating the arm only within the set range of the related art prevents the arm 3 from rotating above the predetermined angle by contacting a wiper fixture 6 rotating together with the arm 3 while being fixed to the arm 3 with the case 1 forming the space in which the filling solution is filled, as shown in FIG. 3.
That is, when the wiper fixture 6 contacts a first rotation prevention part 1a or a second rotation prevention part 1b of the case 1, the arm 3 no longer rotates, such that the arm rotates only within the space range between the first rotation prevention part 1a and the second rotation prevention part 1b. 
However, deviations in the size of the wiper fixture and the case may occur since the wiper fixture 6 and the case 1 are manufactured by an injection molding, such that the case in which the arm 3 exceedingly rotates may often occur.